If you fire one shell at each 8 sec you fire 7 shells that mean 2450 damage/min
Then you don’t have to wait for all drum to be loaded.
Each shell in drum has a different loading time. I don’t see in here this times.
Perhaps is something like 8/10/12/14.

So if you fire entire drum you have to wait for ~14 sec to fire first shell, or you wait 26 to have 2 shells to fire, or 36 for 3 shells and so on.

Let’s consider fighting with a TVP.
tvp empty drum in 5s and wait for 24s
you need 12 s + 14s for one next shell to get tvp .

with BC it is at the limit because avg drum damage capability is 1950, higher than current HP of the spaghetti 65. Maybe buff a litle hp+armour will make things more interesting.